Advanced techniques of plasticating extrusion can produce materials of optimized anisotropic properties and very fine dimensional characteristics. Availability of such materials then supports development of unique polymeric medical devices, such as the everting catheter. Unique polymer resins are first characterized specifically for extrusion characteristics, and predictive models of rheological behavior are constructed. Die designs can now be implemented to take advantage of unique polymer character and to overcome the most critical processing difficulties. The models may also be used to eliminate certain polymers from consideration. Current efforts are to optimize the catheter material for maximally safe operation and to allow development for arterial dilatation.